The disclosure of Japanese Patent Application No. 2000-361076 filed on Nov. 28, 2000 and No. 2001-278724 filed on Sep. 13, 2001 including the specification, drawings and abstract is incorporated herein by reference in their entireties.
1. Field of Invention
The invention relates to a fuel cell output characteristic estimation apparatus and an output characteristic estimation method, a fuel cell system and a vehicle having the same, and a fuel cell output control method and a data storage medium that stores a program to implement the method. More particularly, the invention relates to an output characteristic estimation apparatus that estimates an output characteristic of a fuel cell and an output characteristic estimation method for estimating an output characteristic of a fuel cell, a fuel cell system having a fuel cell and a vehicle having the fuel cell system, and a fuel cell output control method for controlling an output of the fuel cell and a data storage medium that stores a computer-readable program that causes a computer to function as a fuel cell output characteristic arithmetic unit and/or a control unit for the fuel cell system.
2. Description of Related Art
There has been proposed a fuel cell system provided with a commercial power supply or other power generating device that supplies electric power to and receives the electric power from the fuel cell in case of short or excessive supply of the output generated by the fuel cell (see, for example, JP-A-3-80316). In this system, when a power consumption of a load is within a predetermined range of the power that can be supplied by the fuel cell, all the power consumption of the load is covered by the power generated by the fuel cell. When the power consumption of the load exceeds the predetermined range, the excessive part of the power requirement is covered by a DC power obtained by rectifying the power supplied by a commercial power supply or other power generating device. As a result, the fuel cell is ensured to be effectively used.
In the aforementioned type of the fuel cell system, however, owing to a change in the output characteristic of the fuel cell as it has been used for an extended period of time, it may happen that the entire power consumption of the load cannot be covered by the fuel cell even when it is determined that the power consumption of the load is within the predetermined range of the power supplied by the fuel cell. An energy efficiency of the fuel cell also changes at different operation points depending on an output characteristic. Therefore, the output characteristic has to be taken into account when an overall energy efficiency of the entire system is considered.
The applicant of the invention has proposed a system that determines a fuel cell output by taking account of the output characteristic of the fuel cell for the purpose of enhancing an energy efficiency of the fuel cell system (see JP-A-2000-12059).
It is an object of the invention to provide a fuel cell output characteristic estimation apparatus and a fuel cell output characteristic estimation method so as to accurately estimate the output characteristic that is likely to change as the fuel cell has been used for an extended period of time.
It is another object of the invention to provide a fuel cell system and a fuel cell output control method so as to enhance an overall energy efficiency by optimizing the operation of the fuel cell.
It is a further object of the invention to provide a vehicle including the fuel cell system that provides the enhanced energy efficiency.
It is a still further object of the invention to provide a data storage medium that allows a computer to function as a fuel cell output characteristic arithmetic unit for accurately deriving the output characteristic of the fuel cell that varies with time of use, and to function as a control unit for the fuel cell system for enhancing an overall energy efficiency by optimizing the operation of the fuel cell.
A fuel cell output characteristic estimating apparatus for estimating an output characteristic of a fuel cell according to one aspect of the invention includes a current-voltage detector that detects an output current of the fuel cell and a voltage between terminals of the fuel cell, and a controller that estimates the output characteristic of the fuel cell on the basis of the detected output current and the detected voltage between the terminals, detected by the current-voltage detector, and a basic output characteristic of the fuel cell.
The aforementioned fuel cell output characteristic estimation apparatus allows accurate estimation of an output characteristic at a specific timing of a fuel cell that has been used over an extended period of time on the basis of the detected output current, the detected voltage between terminals, and the basic output characteristic of the fuel cell. In this case, the output characteristic of the fuel cell represents a relationship between the output current of the fuel cell and the output voltage of the fuel cell.
In the aforementioned fuel cell output characteristic estimating apparatus, the controller derives the basic output characteristic from at least one of a fuel supply pressure applied to the fuel cell and a temperature of the fuel cell. In this apparatus, the controller derives the basic output characteristic from an output characteristic of the fuel cell corresponding to at least one of the fuel supply pressure applied to the fuel cell and the temperature of the fuel cell, and an internal resistance of the fuel cell corresponding to the temperature of the fuel cell. As a result, the apparatus makes it possible to estimate the output characteristic of the fuel cell more appropriately.
In the aforementioned fuel cell output characteristic estimation apparatus, the controller estimates an internal resistance of the fuel cell on the basis of the detected output current and the detected voltage between the terminals, and the basic output characteristic, and estimates the output characteristic of the fuel cell on the basis of the estimated internal resistance of the fuel cell. This may allow more appropriate estimation of the output characteristic of the fuel. In this apparatus, the controller estimates the output characteristic of the fuel cell on the basis of the output characteristic corresponding to at least one of the fuel supply pressure applied to the fuel cell and the temperature of the fuel cell, and the estimated internal resistance.
According to another aspect of the invention, a fuel cell system having a fuel cell includes a fuel cell output characteristic estimating apparatus for estimating an output characteristic of the fuel cell, including a current-voltage detector that detects an output current of the fuel cell and a voltage between terminals of the fuel cell, and a controller that estimates the output characteristic of the fuel cell on the basis of the detected output current and the detected voltage between the terminals, detected by the current-voltage detector, and a basic output characteristic of the fuel cell; sets a target output of the fuel cell using the output characteristic of the fuel cell estimated by the controller; and adjusts an output of the fuel cell such that the set target output is generated by the fuel cell.
The aforementioned fuel cell system controls the output of the fuel cell using a more optimized fuel cell output characteristic, resulting in an efficient operation of the fuel cell. Accordingly an energy efficiency of the entire system can be enhanced.
The aforementioned fuel cell system includes a power supply that supplies electric power to and receives the electric power from the fuel cell system, in which the controller sets the target output of the fuel cell on the basis of an output required to be generated by the fuel cell system. When the set target output of the fuel cell is in excess of or short of the required output of the fuel cell system, the controller is operable to control (i.e., change) supply of the electric power to or from the power supply. Such arrangement allows the fuel cell system to generate a required amount of electric power while operating the fuel cell efficiently. In the aforementioned fuel cell system, the controller includes a transformer that is connected to terminals of the power supply and transforms the voltage between the terminals of the power supply so as to be applied to output terminals of the fuel cell.
In the aforementioned fuel cell system according to the invention, the controller changes the voltage between the terminals of the fuel cell into a voltage corresponding to the set target output. The use of a more optimized output characteristic of the fuel cell allows the fuel cell to generate a required output by controlling a voltage between terminals of the fuel cell into a voltage corresponding to the required output.
According to another aspect of the invention, a vehicle includes a fuel cell system having a fuel cell output characteristic estimating apparatus for estimating an output characteristic of the fuel cell, including a current-voltage detector that detects an output current of the fuel cell and a voltage between terminals of the fuel cell, and a controller that estimates the output characteristic of the fuel cell on the basis of the detected output current and the detected voltage between the terminals, detected by the current-voltage detector, and a basic output characteristic of the fuel cell. The controller sets a target output of the fuel cell using the output characteristic of the fuel cell estimated by the controller, and adjusts an output of the fuel cell such that the set target output is generated by the fuel cell. Since the fuel cell system uses a more optimized output characteristic of the fuel cell to adjust the output from the fuel cell for the efficient operation of the fuel cell, the vehicle having this type of the fuel cell system may achieve a high energy efficiency.
A method of estimating an output characteristic of a fuel cell according to another aspect of the invention includes the steps of (a) estimating a basic output characteristic of the fuel cell on the basis of at least one of a fuel supply pressure applied to the fuel cell and a temperature of the fuel cell; and (b) estimating the output characteristic of the fuel cell on the basis of the estimated basic output characteristic of the fuel cell, a detected output current of the fuel cell, and a detected voltage between terminals of the fuel cell.
In the aforementioned fuel cell output characteristic estimation method, it is possible to estimate an output characteristic at a specific timing of the fuel cell that has been used over an extended period of time on the basis of the basic output characteristic of the fuel cell obtained from the fuel supply pressure applied to the fuel cell, the temperature of the fuel cell, the detected output current, and the detected voltage between terminals of the fuel cell.
In the aforementioned fuel cell output characteristic estimation method, the basic output characteristic of the fuel cell is estimated using an output characteristic corresponding to at least one of the fuel supply pressure applied to the fuel cell and the temperature of the fuel cell, and an internal resistance of the fuel cell corresponding to the temperature of the fuel cell. This allows the fuel cell output characteristic to be estimated even more appropriately.
In the aforementioned fuel cell output characteristic estimation method, the output characteristic of the fuel cell is estimated using an internal resistance of the fuel cell estimated on the basis of the detected output current, the detected voltage between the terminals of the fuel cell, and the basic output characteristic. This allows the fuel cell output characteristic to be estimated more appropriately. In the aforementioned method, the output characteristic of the fuel cell is estimated using an output characteristic corresponding to at least one of the fuel supply pressure applied to the fuel cell and the temperature of the fuel cell, and the estimated internal resistance of the fuel cell.
A method of controlling an output of a fuel cell according to another aspect of the invention includes the steps of (a) setting a target output using an estimated output characteristic of the fuel cell, wherein the output characteristic of the fuel cell is estimated by the steps of (i) estimating a basic output characteristic of the fuel cell on the basis of at least one of a fuel supply pressure applied to the fuel cell and a temperature of the fuel cell, and (ii) estimating the output characteristic of the fuel cell on the basis of the estimated basic output characteristic of the fuel cell, a detected output current of the fuel cell, and a detected voltage between terminals of the fuel cell; and (b) controlling an output of the fuel cell such that the fuel cell generates the set target output.
According to the aforementioned fuel cell output control method of the invention, even more optimized output characteristic of the fuel cell is estimated and the output of the fuel cell is controlled by using the estimated output characteristic, which allows the fuel cell to be operated efficiently.
In the aforementioned fuel cell output control method, a target output is set on the basis of an output required to be generated by a fuel cell system including a power supply that supplies electric power to and receives the electric power from the fuel cell system, and when the set target output of the fuel cell is in excess of or short of the required output of the fuel cell system, supply of the electric power to or from the power supply is changed. This allows the fuel cell system to generate an output corresponding to an output requirement for the fuel cell system, while operating the fuel cell efficiently. In the fuel cell output control method, a voltage between the terminals of the power supply connected to output terminals of the fuel cell is transformed such that the voltage between the terminals of the fuel cell becomes a voltage corresponding to the target output.
According to another aspect of the invention, a data storage medium that stores a computer readable program that causes a computer to function as a controller for computing an output characteristic of a fuel cell includes a computing program that derives a basic output characteristic of the fuel cell on the basis of at least one of a fuel supply pressure applied to the fuel cell and a temperature of the fuel cell; and derives the output characteristic of the fuel cell on the basis of the derived basic output characteristic of the fuel cell, a detected output current of the fuel cell, and a detected voltage between terminals of the fuel cell.
The aforementioned data storage medium allows a computer to serve as a fuel cell output characteristic arithmetic unit that is capable of computing the output characteristic at a specific timing of a fuel cell which has been used for an extended period of time, on the basis of the detected output current, the detected voltage between terminals of the fuel cell, and the fuel cell basic output characteristic.
In the aforementioned data storage medium, the computing program derives the basic output characteristic using an output characteristic corresponding to at least one of the fuel supply pressure applied to the fuel cell and the temperature of the fuel cell, and an internal resistance of the fuel cell corresponding to the temperature of the fuel cell
In the aforementioned data storage medium, the computing program estimates the output characteristic of the fuel cell using an internal resistance of the fuel cell estimated on the basis of the detected output current, the detected voltage between the terminals of the fuel cell, and the basic output characteristic. In this data storage medium, the computing program derives the output characteristic of the fuel cell using an output characteristic corresponding to at least one of the fuel supply pressure applied to the fuel cell and the temperature of the fuel cell, and the estimated internal resistance.
According to another aspect of the invention, a data storage medium that stores a computer readable program that causes a computer to function as a device for controlling a fuel cell includes a computing program that derives a basic output characteristic of the fuel cell on the basis of at least one of a fuel supply pressure applied to the fuel cell and a temperature of the fuel cell; derives the output characteristic of the fuel cell on the basis of the derived basic output characteristic of the fuel cell, a detected output current of the fuel cell, and a detected voltage between terminals of the fuel cell; sets a target output of the fuel cell using the derived output characteristic of the fuel cell; and controls the output of the fuel cell such that the fuel cell generates the set target output.
The aforementioned data storage medium allows the computer to serve as a control unit for the fuel cell system for controlling the output of the fuel cell using more optimized fuel cell output characteristic so as to operate the fuel cell efficiently.
In the aforementioned data storage medium, the computing program sets the target output on the basis of the output required to be generated by the fuel cell system including the power supply that supplies electric power to and receives the electric power from the fuel cell, and to change the supply of the electric power to or from the power supply when the set target output of the fuel cell is in excess of or short of the required output of the fuel cell system. In this data storage medium, the computing program can cause the transformation of the voltage between the terminals of the power supply connected to the output terminals of the fuel cell such that the voltage between terminals of the fuel cell becomes a voltage corresponding to the set target output.